CN104215952A - Vehicle-mounted target identification system based on micro-motion characteristics and identification method thereof - Google Patents

Vehicle-mounted target identification system based on micro-motion characteristics and identification method thereof Download PDF

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CN104215952A
CN104215952A CN201410428475.0A CN201410428475A CN104215952A CN 104215952 A CN104215952 A CN 104215952A CN 201410428475 A CN201410428475 A CN 201410428475A CN 104215952 A CN104215952 A CN 104215952A
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frequency
signal
target
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msub
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CN104215952B (en
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王敏
陈景东
王勇
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Changshu Southeast High Tech Venture Service Co ltd
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Suzhou Wenjie Sensing Technology Co ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/06—Systems determining position data of a target
    • G01S13/08—Systems for measuring distance only
    • G01S13/32—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
    • G01S13/34—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
    • G01S13/345—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal using triangular modulation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/50—Systems of measurement based on relative movement of target
    • G01S13/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
    • G01S13/583—Velocity or trajectory determination systems; Sense-of-movement determination systems using transmission of continuous unmodulated waves, amplitude-, frequency-, or phase-modulated waves and based upon the Doppler effect resulting from movement of targets
    • G01S13/584—Velocity or trajectory determination systems; Sense-of-movement determination systems using transmission of continuous unmodulated waves, amplitude-, frequency-, or phase-modulated waves and based upon the Doppler effect resulting from movement of targets adapted for simultaneous range and velocity measurements
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
    • G01S7/415—Identification of targets based on measurements of movement associated with the target

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Signal Processing (AREA)
  • Radar Systems Or Details Thereof (AREA)

Abstract

The invention belongs to the technical field of vehicle target identification, and particularly relates to a vehicle-mounted target identification system based on micro-motion characteristics and an identification method thereof. The vehicle-mounted target recognition system based on the inching characteristics comprises: the system comprises a signal transmitting module, a signal receiving module, an analog-to-digital converter, a digital signal processor and a display, wherein the signal transmitting module is installed in front of a vehicle; the input end of the analog-to-digital converter is electrically connected with the output end of the signal receiving module, and the output end of the analog-to-digital converter is electrically connected with the input end of the digital signal processor; the output end of the digital signal processor is electrically connected with the display.

Description

Vehicle-mounted target identification system based on micro-motion characteristics and identification method thereof
Technical Field
The invention belongs to the technical field of vehicle target identification, and particularly relates to a vehicle-mounted target identification system based on micro-motion characteristics and an identification method thereof, which can be used for identifying vehicles and pedestrians in a driving environment.
Background
The active traffic safety detection system can effectively avoid the traffic safety problems caused by factors such as driver negligence, abnormal weather, night driving and the like. The vehicle-mounted detection system acquires target information, can find dangerous targets in advance and give an alarm by using detection results, and simultaneously enables drivers to have sufficient reaction time to avoid accidents as much as possible. The existing vehicle-mounted detection system usually adopts millimeter wave radar. The millimeter wave radar firstly transmits frequency modulation continuous wave signals, and then the distance and speed information of a target is extracted through received echoes. Drivers need to have better judgment on driving environment and target information, and therefore, need to effectively identify different targets.
Currently, target recognition is divided into target recognition based on structural features and target recognition based on high-resolution range profiles. The target identification method based on the structural features mainly utilizes the structural features of the target, such as length, width, thickness and other features with obvious geometric characteristics. The target identification method based on the high-resolution range profile mainly utilizes the range profile of the echo characteristic of a target. The method is mainly suitable for pulse system radars and has low recognition rate for vehicles and pedestrians.
Disclosure of Invention
The invention aims to provide a vehicle-mounted target recognition system based on micro characteristics and a recognition method thereof. The invention is suitable for a vehicle-mounted system, can provide more detailed driving environment and target information for a driver, and can effectively identify vehicles and pedestrians in the driving environment.
The idea of the invention is as follows: the micro-doppler frequency is the manifestation of the motion of the target or micro-moving parts on the target in the radar target echo. Therefore, the micro Doppler information in the radar target echo is analyzed and processed, and the relevant information of the target or the movement form of the micro movement component on the target can be obtained. Because different types of targets determine the difference of micro-motion forms, the time-frequency analysis of the micro-Doppler signals is helpful for extracting information about target classes, thereby realizing the judgment of the target classes. According to the invention, the characteristic frequency is obtained through micro Doppler time frequency analysis, so that the vehicles and the pedestrians can be effectively identified.
In order to achieve the technical purpose, the invention is realized by adopting the following technical scheme.
The first technical scheme is as follows:
the vehicle-mounted target recognition system based on the inching characteristic is characterized by comprising the following components: the system comprises a signal transmitting module, a signal receiving module, an analog-to-digital converter, a digital signal processor and a display, wherein the signal transmitting module is installed in front of a vehicle; the input end of the analog-to-digital converter is electrically connected with the output end of the signal receiving module, and the output end of the analog-to-digital converter is electrically connected with the input end of the digital signal processor; the output end of the digital signal processor is electrically connected with the display.
The technical scheme has the characteristics and further improvement that:
the vehicle-mounted target identification system based on the micro-motion characteristic further comprises a triangular wave generator used for generating periodic triangular waves, and the signal transmitting module comprises a transmitting antenna, a carrier signal source and a frequency mixer; two input ends of the frequency mixer are correspondingly and electrically connected with a triangular wave generator and a carrier signal source;
the signal receiving module comprises a receiving antenna, a signal distributor, a 90-degree phase shifter, a first frequency converter and a second frequency converter; the input end of the signal distributor is electrically connected with the receiving antenna, the two output ends of the signal distributor are correspondingly and electrically connected with the first input end of the first frequency converter and the first input end of the second frequency converter, the output end of the frequency mixer is respectively and electrically connected with the transmitting antenna, the second input end of the first frequency converter and the input end of the 90-degree phase shifter, the output end of the 90-degree phase shifter is electrically connected with the second input end of the second frequency converter, and the input end of the analog-to-digital converter is respectively and electrically connected with the output end of the first frequency converter and the output end of the second frequency converter.
A first anti-leakage filter and a first low-pass filter are sequentially connected between the first frequency converter and the analog-to-digital converter in series, and a second anti-leakage filter and a second low-pass filter are sequentially connected between the second frequency converter and the analog-to-digital converter in series; the output end of the first frequency converter is electrically connected with the input end of the first anti-leakage filter, and the output end of the second frequency converter is electrically connected with the input end of the second anti-leakage filter; the output end of the first anti-leakage filter is electrically connected with the input end of the first low-pass filter, and the output end of the second anti-leakage filter is electrically connected with the input end of the second low-pass filter; and the input end of the analog-to-digital converter is respectively and electrically connected with the output end of the first low-pass filter and the output end of the second low-pass filter.
The second technical scheme is as follows:
the target identification method based on the inching characteristic is based on the vehicle-mounted target identification system based on the inching characteristic, and is characterized by comprising the following steps of:
s1: the signal transmitting module transmits radio frequency signals to the front of the vehicle and transmits the radio frequency signals to the signal receiving module;
s2: the signal receiving module receives an echo signal, and then generates an I channel difference frequency analog signal and a Q channel difference frequency analog signal which are orthogonal to each other according to the radio frequency signal and the echo signal;
s3: the analog-to-digital converter respectively performs analog-to-digital conversion on the I channel difference frequency analog signal and the Q channel difference frequency analog signal, and sends an I channel difference frequency digital signal and a Q channel difference frequency digital signal obtained by the analog-to-digital conversion to the digital signal processor;
s4: the digital signal processor combines the I channel difference frequency digital signal and the Q channel difference frequency digital signal into an echo fundamental frequency signal; whether a target appears at a corresponding moment is judged by carrying out constant false alarm detection on the echo fundamental frequency signal; the target is a vehicle or a pedestrian;
s5: when a target appears at the corresponding moment, the digital signal processor obtains the speed of the corresponding target; and then, obtaining the category of the corresponding target according to the speed of the corresponding target.
The technical scheme has the characteristics and further improvement that:
the vehicle-mounted target identification system based on the micro-motion characteristic further comprises a triangular wave generator used for generating periodic triangular waves, and the signal transmitting module comprises a transmitting antenna, a carrier signal source and a mixer; two input ends of the frequency mixer are correspondingly and electrically connected with a triangular wave generator and a carrier signal source; the signal receiving module comprises a receiving antenna, a signal distributor, a 90-degree phase shifter, a first frequency converter and a second frequency converter;
the input end of the signal distributor is electrically connected with a receiving antenna, the two output ends of the signal distributor are correspondingly and electrically connected with the first input end of a first frequency converter and the first input end of a second frequency converter, the output end of the frequency mixer is respectively and electrically connected with a transmitting antenna, the second input end of the first frequency converter and the input end of a 90-degree phase shifter, and the output end of the 90-degree phase shifter is electrically connected with the second input end of the second frequency converter; the input end of the analog-to-digital converter is respectively and electrically connected with the output end of the first frequency converter and the output end of the second frequency converter;
in step S1, the triangular wave generator generates a periodic triangular wave, and generates a periodic chirp continuous wave according to the triangular wave, where the period of the chirp continuous wave is the period of the triangular wave, and the amplitude of the triangular wave is used to control the frequency of the chirp continuous wave; then, transmitting the linear frequency modulation continuous wave to the mixer; the carrier signal source generates a carrier signal and transmits the carrier signal to the mixer; the frequency mixer mixes the linear frequency modulation continuous wave and the carrier signal to obtain a radio frequency signal, and then the radio frequency signal is respectively sent to the transmitting antenna, the first frequency converter and the 90-degree phase shifter; and the transmitting antenna transmits the radio frequency signal to the front of the vehicle.
In step S2, the receiving antenna receives the echo signal and sends the echo signal to the first frequency converter and the second frequency converter respectively, the 90-degree phase shifter performs 90-degree phase shifting on the radio frequency signal, and sends the phase-shifted signal to the second frequency converter; the first frequency converter carries out frequency mixing processing on the echo signal and the radio frequency signal to obtain an I channel difference frequency analog signal; and the second frequency converter performs frequency mixing processing on the echo signal and the phase-shifted signal to obtain a Q channel difference frequency analog signal.
In step S3, the I channel difference frequency analog signal is represented as I (t), t is a discrete time variable, and the Q channel difference frequency analog signal is represented as Q (t);
in step S4, the digital signal processor combines the I channel difference frequency digital signal I (t) and the Q channel difference frequency digital signal Q (t) into the echo fundamental frequency signal S (t);
in step S4, the distance R of the target and the velocity v of the target are derived:
<math> <mrow> <mi>R</mi> <mo>=</mo> <mfrac> <mi>c</mi> <mrow> <mn>4</mn> <mi>&Delta;f</mi> </mrow> </mfrac> <mfrac> <mrow> <msubsup> <mi>f</mi> <mi>b</mi> <mo>+</mo> </msubsup> <mo>+</mo> <msubsup> <mi>f</mi> <mi>b</mi> <mo>-</mo> </msubsup> </mrow> <mrow> <mn>2</mn> <mi>T</mi> </mrow> </mfrac> </mrow> </math>
v = c ( f b + - f b - ) 4 f 0
where c is the speed of light, Δ f is the maximum frequency offset of the chirped continuous wave, f0Is the center frequency of the chirped continuous wave,forward frequency modulation is used to beat the signal frequency,the beat signal frequency is the negative frequency modulation,andrespectively as follows:
f b + = f t - f r , f b - = f r - f t
wherein f istIs the frequency of the radio frequency signal, frIs the frequency of the echo signal;
in step S5, the speed v of the object is determined, and when the speed v of the object exceeds a set speed threshold, the type of the object is a vehicle; and conversely, when the speed v of the target is less than or equal to the set speed threshold value, the target is classified as a pedestrian.
In step S5, when a target appears at the corresponding time, the digital signal processor performs time-frequency analysis on the corresponding fundamental echo frequency signal to obtain a time-frequency spectrum S (t, f) of the corresponding fundamental echo frequency signal, where S (t, f) is:
S(t,f)＝∫s(τ)·w(τ-t)·exp(-j2πfτ)dτ
where f denotes a discrete frequency variable, τ a time integral variable, w (t) denotes a window function,
then, a time-frequency graph corresponding to the echo fundamental frequency signal is obtained, and the time-frequency graph corresponding to the echo fundamental frequency signal is a time-frequency graph obtained after S (t, f) discretization;
then, according to the discretized time-frequency graph of S (t, f), obtaining the time-frequency characteristics of the corresponding target, wherein the time-frequency characteristics of the corresponding target are time-frequency entropy f1Or entropy f of the mean instantaneous Doppler spectrum of the corresponding target2，f1Comprises the following steps:
<math> <mrow> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo>=</mo> <mo>-</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>M</mi> </munderover> <munderover> <mi>&Sigma;</mi> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>N</mi> </munderover> <msub> <mi>p</mi> <mi>ij</mi> </msub> <msub> <mi>log</mi> <mn>10</mn> </msub> <msub> <mi>p</mi> <mi>ij</mi> </msub> </mrow> </math>
wherein i and j respectively represent pixel points at the ith row and the jth column position in the time-frequency diagram corresponding to the echo fundamental frequency signal, M and N are respectively the row number and the column number of the time-frequency diagram corresponding to the echo fundamental frequency signal,S(ti,fj) Representing the energy of a pixel point at the ith row and the jth column position in a time-frequency diagram corresponding to the echo fundamental frequency signal;
f2comprises the following steps:
<math> <mrow> <msub> <mi>f</mi> <mn>2</mn> </msub> <mo>=</mo> <mo>-</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>K</mi> </munderover> <msub> <mi>&rho;</mi> <mi>k</mi> </msub> <msub> <mi>log</mi> <mn>10</mn> </msub> <msub> <mi>&rho;</mi> <mi>k</mi> </msub> </mrow> </math>
wherein,F(fk) Is the kth Fourier transform value of F (f),k is the number of fast Fourier transform points of g (t), S (t, f)k) A column vector formed by all energy values of the kth column in the time-frequency diagram corresponding to the echo fundamental frequency signal, | S (t, f)k) I denotes the pair S (t, f)k) And (6) taking a mold.
In step S5, after the time-frequency entropies of the l targets are obtained through accumulation, a corresponding training sample is obtained according to the time-frequency entropy of each target; when the time-frequency characteristic of the corresponding target is the time-frequency entropy f1When the time-frequency characteristic of the corresponding target is the entropy f of the average instantaneous Doppler spectrum of the corresponding target, the term "M × N" refers to2When l is K; the ith training sample includes: time-frequency characteristic x of ith targetiAnd classification label y of ith targetiI takes 1 to l; when the speed of the ith target exceeds the set speed threshold, yi1, otherwise yi＝-1；
The following optimization problem is then solved:
<math> <mfenced open='' close=''> <mtable> <mtr> <mtd> <munder> <mi>min</mi> <mrow> <mi>w</mi> <mo>,</mo> <mi>b</mi> </mrow> </munder> </mtd> <mtd> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msup> <mrow> <mo>|</mo> <mo>|</mo> <mi>w</mi> <mo>|</mo> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>,</mo> </mtd> </mtr> <mtr> <mtd> <mi>s</mi> <mo>.</mo> <mi>t</mi> <mo>.</mo> </mtd> <mtd> <msub> <mi>y</mi> <mi>i</mi> </msub> <mo>[</mo> <mrow> <mo>(</mo> <mi>w</mi> <mo>&CenterDot;</mo> <msub> <mi>x</mi> <mi>i</mi> </msub> <mo>)</mo> </mrow> <mo>+</mo> <mi>b</mi> <mo>]</mo> <mo>&GreaterEqual;</mo> <mn>1</mn> <mo>,</mo> <mi>i</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>,</mo> <mi>l</mi> </mtd> </mtr> </mtable> </mfenced> </math>
w and b are two parameters (scalars) to be solved, and w represents the absolute value of w;
if (w.x)i)+b)>And 0, the ith target is a vehicle target, otherwise, the ith target is a pedestrian target.
The invention has the beneficial effects that: first, the present invention is applicable to an on-vehicle detection system, and can provide more detailed driving environment and target information to a driver. Secondly, the method can effectively identify the vehicles and pedestrians in the driving environment through time-frequency analysis based on the micro Doppler characteristics of the target.
Drawings
FIG. 1 is a schematic diagram of the present invention showing the structure of a vehicle-mounted target recognition system based on the inching characteristic;
FIG. 2 is a flow chart of the present invention for a vehicle target identification method based on inching characteristics;
FIG. 3 is a schematic diagram showing the relationship between a triangular wave generated by a triangular wave generator and a chirp continuous wave in the present invention;
FIG. 4 is a flow chart of constant false alarm detection in an embodiment of the present invention;
FIG. 5 is a flowchart illustrating the determination of the target class according to the present invention;
fig. 6 is a schematic diagram of the result of the multi-scattering point constant false alarm detection obtained by the simulation experiment.
Detailed Description
The invention will be further described with reference to the accompanying drawings in which:
referring to fig. 1, a schematic diagram of a vehicle-mounted object recognition system based on inching characteristics is shown. The vehicle-mounted target recognition system based on the inching characteristics comprises: the system comprises a signal transmitting module installed in the front of the vehicle, a signal receiving module installed in the front of the vehicle, an analog-to-digital converter arranged on the vehicle, a digital signal processor (DSP chip) arranged on the vehicle and a display installed on a vehicle console. The input end of the analog-to-digital converter is electrically connected with the output end of the signal receiving module, and the output end of the analog-to-digital converter is electrically connected with the input end of the digital signal processor; the output end of the digital signal processor is electrically connected with the display.
In the embodiment of the invention, a triangular wave generator for generating a periodic triangular wave is further arranged, the triangular wave generator generates a linear frequency modulation continuous wave according to the amplitude of the generated periodic triangular wave, wherein the period of the triangular wave is the period of the frequency modulation continuous wave. The signal transmitting module comprises a transmitting antenna, a carrier signal source and a mixer; two input ends of the frequency mixer are correspondingly and electrically connected with a triangular wave generator and a carrier signal source; the frequency mixer is used for carrying out frequency mixing processing on the carrier signal generated by the carrier signal source and the frequency modulation continuous wave to generate two paths of same signals. The output end of the frequency mixer is respectively and electrically connected with the transmitting antenna, the second input end of the first frequency converter and the input end of the 90-degree phase shifter, for two paths of same signals generated by the frequency mixer, one path of signals are used as transmitting signals to be transmitted outwards (transmitted outwards through the transmitting antenna), and the other path of signals are transmitted to the signal receiving part (namely the 90-degree phase shifter and the first frequency converter).
The signal receiving module comprises a receiving antenna, a signal distributor, a 90-degree phase shifter, a first frequency converter and a second frequency converter; the input end of the signal distributor is electrically connected with the receiving antenna, the two output ends of the signal distributor are correspondingly and electrically connected with the first input end of the first frequency converter and the first input end of the second frequency converter, and the signal distributor sends the received echo signals to the first frequency converter and the second frequency converter respectively. The output end of the 90-degree phase shifter is electrically connected with the second input end of the second frequency converter, the 90-degree phase shifter performs 90-degree phase shifting processing on the received signal, and then the signal subjected to the 90-degree phase shifting processing is transmitted to the second frequency converter. Each frequency converter carries out down-conversion processing on the two groups of received signals, wherein the first frequency converter generates I channel difference frequency analog signals, and the second frequency converter generates Q channel difference frequency analog signals. The input end of the analog-to-digital converter is electrically connected with the output end of the first frequency converter and the output end of the second frequency converter respectively, the analog-to-digital converter is used for performing analog-to-digital conversion on received signals (sampling an I channel difference frequency analog signal and a generated Q channel difference frequency analog signal respectively), and the output end of the analog-to-digital converter is electrically connected with the input end of the digital signal processor, so that the digital signal processor receives the signals after the analog-to-digital conversion.
In the embodiment of the invention, a digital signal processor combines received signals into echo fundamental frequency signals, and then distance and speed information of a target is obtained through constant false alarm detection; meanwhile, the echo fundamental frequency signal is subjected to time-frequency analysis, the time-frequency characteristics of the corresponding target are extracted, and the time-frequency characteristics of the corresponding target are transmitted to a Support Vector Machine (SVM) classifier to be judged, so that a target identification result is obtained. The digital signal processor presents the distance and speed information of the target and the target recognition result to the driver, so that the driver can effectively recognize the vehicle and the pedestrian and can make prejudgment.
In the embodiment of the invention, a first anti-leakage filter and a first low-pass filter are sequentially connected between a first frequency converter and an analog-to-digital converter in series, and a second anti-leakage filter and a second low-pass filter are sequentially connected between a second frequency converter and the analog-to-digital converter in series; the output end of the first frequency converter is electrically connected with the input end of the first anti-leakage filter, and the output end of the second frequency converter is electrically connected with the input end of the second anti-leakage filter; the output end of the first anti-leakage filter is electrically connected with the input end of the first low-pass filter, and the output end of the second anti-leakage filter is electrically connected with the input end of the second low-pass filter; and the input end of the analog-to-digital converter is respectively and electrically connected with the output end of the first low-pass filter and the output end of the second low-pass filter.
The embodiment of the invention also provides a vehicle-mounted target identification method based on the inching characteristic, and the method is a flow chart of the vehicle-mounted target identification method based on the inching characteristic in reference to fig. 2. The vehicle-mounted target identification method based on the inching characteristics takes the vehicle-mounted target identification system based on the inching characteristics as a basis, and comprises the following steps:
s1: the signal transmitting module transmits radio frequency signals to the front of the vehicle and transmits the radio frequency signals to the signal receiving module.
Specifically, the triangular wave generator generates a periodic triangular wave, and generates a periodic chirp continuous wave from the triangular wave, wherein the period of the chirp continuous wave is the period of the triangular wave, and the amplitude of the triangular wave is used for controlling the frequency of the chirp continuous wave. Referring to fig. 3, a schematic diagram of the relationship between the triangular wave generated by the triangular wave generator and the chirped continuous wave is shown. In FIG. 3, the horizontal axis represents the voltage of a triangular wave in the present invention, the vertical axis represents the frequency of a chirp continuous wave, T+Is the positive half cycle duration of the waveform, T-The duration of the negative half cycle of the waveform. As seen from fig. 3, the triangular waveform shows that the voltage increases linearly from 0 at the positive half cycle time point and decreases linearly from the highest value at the negative half cycle time point. The triangular wave generator is mainly realized by a voltage-controlled signal source, the frequency of a signal output by the voltage-controlled signal source changes along with the voltage of an input signal, and the frequency tuning rate is linear.
Then, transmitting the linear frequency modulation continuous wave to the mixer; the carrier signal source generates a carrier signal and transmits the carrier signal to the mixer; the frequency mixer mixes the linear frequency modulation continuous wave and the carrier signal to obtain a radio frequency signal, and then the radio frequency signal is respectively sent to the transmitting antenna, the first frequency converter and the 90-degree phase shifter; and the transmitting antenna transmits the radio frequency signal to the front of the vehicle.
In the embodiment of the invention, the radio frequency signal is constructed by a positive slope frequency modulation signal and a negative slope frequency modulation signal, wherein the positive slope frequency modulation signal s (t)0) And a negative slope FM signal s (t)1) Respectively as follows:
s(t0)＝cos(2π(f0t0+Kt0 2/2))
s(t1)＝cos(2π(f0t1-Kt1 2/2))
where K is the chirp rate of the chirped continuous wave, f0Is the center frequency, t0At positive periodic time points, t1Negative cycle time points.
S2: the signal receiving module receives the echo signal, and then generates an I channel difference frequency analog signal and a Q channel difference frequency analog signal which are orthogonal to each other according to the radio frequency signal and the echo signal.
Specifically, the receiving antenna receives an echo signal (an echo signal of a front target or a scattering point), and sends the echo signal to the first frequency converter and the second frequency converter respectively, the 90-degree phase shifter performs 90-degree phase shift processing on the radio-frequency signal, and sends the phase-shifted signal to the second frequency converter; the first frequency converter carries out frequency mixing processing on the echo signal and the radio frequency signal to obtain an I channel difference frequency analog signal; and the second frequency converter performs frequency mixing processing on the echo signal and the phase-shifted signal to obtain a Q channel difference frequency analog signal.
In the embodiment of the invention, the Doppler frequency shift f of the echo signal received by the receiving antennadComprises the following steps:
f d = 2 f 0 v c
where v denotes the target speed and c is the speed of light.
Delay effect f of echo signals received by a receiving antennadelayComprises the following steps:
<math> <mrow> <msub> <mi>f</mi> <mi>delay</mi> </msub> <mo>=</mo> <mfrac> <mrow> <mn>4</mn> <mi>R&Delta;f</mi> </mrow> <mi>cT</mi> </mfrac> </mrow> </math>
wherein, R represents the distance between the target and the vehicle, T is the period of the frequency modulation continuous wave, and delta f is the maximum frequency deviation of the frequency modulation continuous wave.
S3: the analog-to-digital converter respectively carries out analog-to-digital conversion on the I channel difference frequency analog signal and the Q channel difference frequency analog signal, and sends the I channel difference frequency digital signal and the Q channel difference frequency digital signal obtained by the analog-to-digital conversion to the digital signal processor.
Specifically, in step S3, the I channel difference frequency analog signal is represented as I (t), t is a discrete time variable, and the Q channel difference frequency analog signal is represented as Q (t); when t is the positive half cycle waveform duration of the I channel difference frequency analog signal (positive half cycle waveform duration of the Q channel difference frequency analog signal), the specific forms of I (t) and Q (t) are respectively:
I(t)＝Acos(πKt2)
Q(t)＝Asin(πKt2)
when t is the duration of the negative half cycle waveform of the I channel difference frequency analog signal (the duration of the negative half cycle waveform of the Q channel difference frequency analog signal), the specific forms of I (t) and Q (t) are respectively:
I(t)＝Acos(-πKt2)
Q(t)＝Asin(-πKt2)
s4: the digital signal processor combines the I channel difference frequency digital signal and the Q channel difference frequency digital signal into an echo fundamental frequency signal; whether a target appears at a corresponding moment is judged by carrying out constant false alarm detection on the echo fundamental frequency signal; the target is a vehicle or a pedestrian;
specifically, the echo fundamental frequency signal is represented as s (t), and when t is the positive half cycle waveform duration of the I channel difference frequency analog signal (the positive half cycle waveform duration of the Q channel difference frequency analog signal), the specific form of s (t) is as follows:
<math> <mrow> <mi>s</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>=</mo> <mi>I</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>+</mo> <mi>jQ</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>=</mo> <msup> <mi>Ae</mi> <msup> <mi>j&pi;Kt</mi> <mn>2</mn> </msup> </msup> </mrow> </math>
when t is the duration of the negative half cycle waveform of the I channel difference frequency analog signal (the duration of the negative half cycle waveform of the Q channel difference frequency analog signal), the specific form of s (t) is as follows:
<math> <mrow> <mi>s</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>=</mo> <mi>I</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>+</mo> <mi>jQ</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>=</mo> <msup> <mrow> <mi>Ae</mi> <mo>-</mo> </mrow> <msup> <mi>j&pi;Kt</mi> <mn>2</mn> </msup> </msup> </mrow> </math>
where K is the chirp rate of the chirped continuous wave and A is a constant (a constant related to the target scattering rate).
In step 4, constant false alarm detection is performed on the echo fundamental frequency signal, and the specific process is as follows:
referring to fig. 4, a flowchart of constant false alarm detection in an embodiment of the present invention is shown. A unit average constant false alarm detector is adopted to send echo fundamental frequency signals s (t) to a delay line formed by 2L +1 delay distance units, a detection distance unit D is positioned at the center position, L distance units are respectively taken as reference units at two sides and respectively correspond to input signals with different discrete time. Summing the s values in all reference units and dividing by 2L to obtain the mean value estimation of the clutter background at the detected unit
<math> <mrow> <mover> <mi>&mu;</mi> <mo>^</mo> </mover> <mo>=</mo> <mfrac> <mn>1</mn> <mrow> <mn>2</mn> <mi>L</mi> </mrow> </mfrac> <munderover> <mi>&Sigma;</mi> <mrow> <mi>t</mi> <mo>=</mo> <mi>D</mi> <mo>-</mo> <mi>L</mi> </mrow> <mrow> <mi>D</mi> <mo>+</mo> <mi>L</mi> </mrow> </munderover> <mi>s</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </mrow> </math>
Wherein the detection thresholdK' is a set threshold multiplier. The threshold U may be changed when the size of the threshold multiplier K' is adjusted0Thereby ensuring the constant false alarm rate. When the input signal (echo fundamental frequency signal s (t)) exceeds the detection threshold, the target appears at the moment corresponding to the detection distance unit DThe target is transmitted to the next step; when the echo fundamental frequency signal s (t) does not reach the threshold, clutter or noise is judged and is not considered.
In step S4, the distance R of the target and the velocity v of the target are derived:
<math> <mrow> <mi>R</mi> <mo>=</mo> <mfrac> <mi>c</mi> <mrow> <mn>4</mn> <mi>&Delta;f</mi> </mrow> </mfrac> <mfrac> <mrow> <msubsup> <mi>f</mi> <mi>b</mi> <mo>+</mo> </msubsup> <mo>+</mo> <msubsup> <mi>f</mi> <mi>b</mi> <mo>-</mo> </msubsup> </mrow> <mrow> <mn>2</mn> <mi>T</mi> </mrow> </mfrac> </mrow> </math>
v = c ( f b + - f b - ) 4 f 0
where c is the speed of light, Δ f is the maximum frequency offset of the chirped continuous wave, f0Is the center frequency of the chirped continuous wave,forward frequency modulation is used to beat the signal frequency,the beat signal frequency is the negative frequency modulation,andrespectively as follows:
f b + = f t - f r , f b - = f r - f t
wherein f istIs the frequency of the radio frequency signal, frIs the frequency of the echo signal.
S5: when a target appears at the corresponding moment, the digital signal processor obtains the speed of the corresponding target; and then, obtaining the category of the corresponding target according to the speed of the corresponding target.
Referring to fig. 5, a flowchart of the target category determination according to the present invention is shown. In step S5, the speed v of the object is determined, and when the speed v of the object exceeds a set speed threshold, the type of the object is a vehicle; and conversely, when the speed v of the target is less than or equal to the set speed threshold value, the target is classified as a pedestrian.
When a target appears at the corresponding moment, the digital signal processor performs time-frequency analysis on the corresponding echo fundamental frequency signal to obtain a time-frequency spectrum S (t, f) of the corresponding echo fundamental frequency signal, wherein S (t, f) is as follows:
S(t,f)＝∫s(τ)·w(τ-t)·exp(-j2πfτ)dτ
where f denotes a discrete frequency variable, τ a time integral variable, w (t) denotes a window function,
then, a time-frequency graph corresponding to the echo fundamental frequency signal is obtained, and the time-frequency graph corresponding to the echo fundamental frequency signal is a time-frequency graph obtained after S (t, f) discretization;
then, according to the discretized time-frequency graph of S (t, f), obtaining the time-frequency characteristics of the corresponding target, wherein the time-frequency characteristics of the corresponding target are time-frequency entropy f1Entropy f of mean instantaneous Doppler spectrum of corresponding target2Or the proportion f of the maximum value of the average instantaneous Doppler spectrum of the corresponding target3，f1Comprises the following steps:
<math> <mrow> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo>=</mo> <mo>-</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>M</mi> </munderover> <munderover> <mi>&Sigma;</mi> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>N</mi> </munderover> <msub> <mi>p</mi> <mi>ij</mi> </msub> <msub> <mi>log</mi> <mn>10</mn> </msub> <msub> <mi>p</mi> <mi>ij</mi> </msub> </mrow> </math>
wherein i and j respectively represent pixel points at the ith row and the jth column position in the time-frequency diagram corresponding to the echo fundamental frequency signal, M and N are respectively the row number and the column number of the time-frequency diagram corresponding to the echo fundamental frequency signal,S(ti,fj) Representing the energy of a pixel point at the ith row and the jth column position in a time-frequency diagram corresponding to the echo fundamental frequency signal;
f2comprises the following steps:
<math> <mrow> <msub> <mi>f</mi> <mn>2</mn> </msub> <mo>=</mo> <mo>-</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>K</mi> </munderover> <msub> <mi>&rho;</mi> <mi>k</mi> </msub> <msub> <mi>log</mi> <mn>10</mn> </msub> <msub> <mi>&rho;</mi> <mi>k</mi> </msub> </mrow> </math>
wherein,F(fk) F (f) FFT (g (t)), f (f) is the fast fourier transform value of g (t),k is the number of fast Fourier transform points of g (t), S (t, f)k) A column vector formed by all energy values of the kth column in the time-frequency diagram corresponding to the echo fundamental frequency signal, | S (t, f)k) I denotes the pair S (t, f)k) And (6) taking a mold. F (f) is the average instantaneous doppler spectrum, for an arbitrary instant t ', the time-frequency spectrum S (t', f) reflects the instantaneous frequencies of all scattering points of the target at that instant. g (t) is a linear combination of the instantaneous frequencies of the scattering points, so the instantaneous frequencies of the scattering points, i.e., F (f), can be obtained by fast Fourier transforming g (t). The instantaneous frequency components contained in the spectrum of the walking human target are more than those of the vehicle, so that the entropy of the average instantaneous frequency spectrum of the vehicle is smaller than that of the walking human target.
f3Comprises the following steps: f. of3Max (p), where,f3the proportion of the maximum value of the average instantaneous doppler spectrum to the total energy is described, and the larger the maximum value is after normalization, the larger the feature three is.
In step S5, after the time-frequency entropies of the l targets are obtained through accumulation, a corresponding training sample is obtained according to the time-frequency entropy of each target; when the time-frequency characteristic of the corresponding target is the time-frequency entropy f1When the time-frequency characteristic of the corresponding target is the entropy f of the average instantaneous Doppler spectrum of the corresponding target, the term "M × N" refers to2When l is K; the ith training sample includes: time-frequency characteristic x of ith targetiAnd classification label y of ith targetiI takes 1 to l; when the speed of the ith target exceeds the set speed threshold, yi1, otherwise yi＝-1；
The following optimization problem is then solved:
<math> <mfenced open='' close=''> <mtable> <mtr> <mtd> <munder> <mi>min</mi> <mrow> <mi>w</mi> <mo>,</mo> <mi>b</mi> </mrow> </munder> </mtd> <mtd> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msup> <mrow> <mo>|</mo> <mo>|</mo> <mi>w</mi> <mo>|</mo> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>,</mo> </mtd> </mtr> <mtr> <mtd> <mi>s</mi> <mo>.</mo> <mi>t</mi> <mo>.</mo> </mtd> <mtd> <msub> <mi>y</mi> <mi>i</mi> </msub> <mo>[</mo> <mrow> <mo>(</mo> <mi>w</mi> <mo>&CenterDot;</mo> <msub> <mi>x</mi> <mi>i</mi> </msub> <mo>)</mo> </mrow> <mo>+</mo> <mi>b</mi> <mo>]</mo> <mo>&GreaterEqual;</mo> <mn>1</mn> <mo>,</mo> <mi>i</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>,</mo> <mi>l</mi> </mtd> </mtr> </mtable> </mfenced> </math>
w and b are two parameters (scalars) to be solved, and w represents the absolute value of w; after w and b are obtained, establishing a classification surface (w · x) + b ═ 0 according to w and b; then, identifying the target class according to the classification surface (w · x) + b ═ 0;
if (w.x)i)+b)>And 0, the ith target is a vehicle target, otherwise, the ith target is a pedestrian target.
The effects of the present invention can be illustrated by the following simulation experiments:
1) simulation conditions
The parameters of the signal transmitting module are as follows: carrier frequency f0At 3GHz, Nyquist sampling rate of 30MHz, observation window of the signal receiving module is 10,2000]And m is selected. The target parameters are: there are 3 scattering points in the observation interval, each located at [600,780,1200 ]]The backscattering coefficients of m and 3 scattering points are respectively 1, 0.5 and 0.8, the scattering point speeds of the 3 scattering points are respectively 100m/s, 60m/s and 15m/s, when constant false alarm detection is carried out, the parameter L is 24, and the theoretical constant false alarm rate is set to be 1 multiplied by 10-6. White Gaussian noise with zero mean background noise and variance of sigma2Defining the signal-to-noise ratio
<math> <mrow> <mi>SNR</mi> <mo>=</mo> <mn>20</mn> <msub> <mi>log</mi> <mn>10</mn> </msub> <mfrac> <mrow> <mi>min</mi> <mrow> <mo>(</mo> <mi>A</mi> <mo>)</mo> </mrow> </mrow> <mi>&sigma;</mi> </mfrac> </mrow> </math>
2) Emulated content
The process of constant false alarm detection by using the simulation parameters is shown in fig. 6, which is a schematic diagram of the result of constant false alarm detection of multiple scattering points obtained by a simulation experiment. In fig. 6, the horizontal axis represents time in units of s, and the vertical axis represents the amplitude of the echo fundamental frequency signal after constant false alarm processing in units of v.
3) Analysis of simulation results
As can be seen from fig. 6, 3 scattering points, i.e. 3 detection targets, can be obtained at the correct positions by constant false alarm detection. If the constant false alarm probability is too low, the detection threshold in the graph can move upwards, so that a second target with a small scattering coefficient is mistakenly considered as clutter or noise and is submerged in the noise, and false alarm is caused; otherwise, the detection threshold may be shifted down, resulting in excessive false alarm.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims (9)

1. The vehicle-mounted target recognition system based on the inching characteristic is characterized by comprising the following components: the system comprises a signal transmitting module, a signal receiving module, an analog-to-digital converter, a digital signal processor and a display, wherein the signal transmitting module is installed in front of a vehicle; the input end of the analog-to-digital converter is electrically connected with the output end of the signal receiving module, and the output end of the analog-to-digital converter is electrically connected with the input end of the digital signal processor; the output end of the digital signal processor is electrically connected with the display.
2. The vehicle-mounted target recognition system based on the inching characteristic of claim 1, further comprising a triangular wave generator for generating a periodic triangular wave, wherein the signal transmitting module comprises a transmitting antenna, a carrier signal source and a mixer; two input ends of the frequency mixer are correspondingly and electrically connected with a triangular wave generator and a carrier signal source;
the signal receiving module comprises a receiving antenna, a signal distributor, a 90-degree phase shifter, a first frequency converter and a second frequency converter; the input end of the signal distributor is electrically connected with the receiving antenna, the two output ends of the signal distributor are correspondingly and electrically connected with the first input end of the first frequency converter and the first input end of the second frequency converter, the output end of the frequency mixer is respectively and electrically connected with the transmitting antenna, the second input end of the first frequency converter and the input end of the 90-degree phase shifter, the output end of the 90-degree phase shifter is electrically connected with the second input end of the second frequency converter, and the input end of the analog-to-digital converter is respectively and electrically connected with the output end of the first frequency converter and the output end of the second frequency converter.
3. The vehicle-mounted target recognition system based on the inching characteristic as claimed in claim 1, wherein a first anti-leakage filter and a first low-pass filter are connected in series between the first frequency converter and the analog-to-digital converter in sequence, and a second anti-leakage filter and a second low-pass filter are connected in series between the second frequency converter and the analog-to-digital converter in sequence; the output end of the first frequency converter is electrically connected with the input end of the first anti-leakage filter, and the output end of the second frequency converter is electrically connected with the input end of the second anti-leakage filter; the output end of the first anti-leakage filter is electrically connected with the input end of the first low-pass filter, and the output end of the second anti-leakage filter is electrically connected with the input end of the second low-pass filter; and the input end of the analog-to-digital converter is respectively and electrically connected with the output end of the first low-pass filter and the output end of the second low-pass filter.
4. The target identification method based on the inching characteristic and the vehicle-mounted target identification system based on the inching characteristic as claimed in claim 1 are characterized by comprising the following steps:
s1: the signal transmitting module transmits radio frequency signals to the front of the vehicle and transmits the radio frequency signals to the signal receiving module;
s2: the signal receiving module receives an echo signal, and then generates an I channel difference frequency analog signal and a Q channel difference frequency analog signal which are orthogonal to each other according to the radio frequency signal and the echo signal;
s3: the analog-to-digital converter respectively performs analog-to-digital conversion on the I channel difference frequency analog signal and the Q channel difference frequency analog signal, and sends an I channel difference frequency digital signal and a Q channel difference frequency digital signal obtained by the analog-to-digital conversion to the digital signal processor;
s4: the digital signal processor combines the I channel difference frequency digital signal and the Q channel difference frequency digital signal into an echo fundamental frequency signal; whether a target appears at a corresponding moment is judged by carrying out constant false alarm detection on the echo fundamental frequency signal; the target is a vehicle or a pedestrian;
s5: when a target appears at the corresponding moment, the digital signal processor obtains the speed of the corresponding target; and then, obtaining the category of the corresponding target according to the speed of the corresponding target.
5. The method for identifying targets based on inching characteristics as claimed in claim 4, wherein the inching characteristic-based vehicle-mounted target identification system further comprises a triangular wave generator for generating a periodic triangular wave, and the signal transmitting module comprises a transmitting antenna, a carrier signal source and a mixer; two input ends of the frequency mixer are correspondingly and electrically connected with a triangular wave generator and a carrier signal source; the signal receiving module comprises a receiving antenna, a signal distributor, a 90-degree phase shifter, a first frequency converter and a second frequency converter;
the input end of the signal distributor is electrically connected with a receiving antenna, the two output ends of the signal distributor are correspondingly and electrically connected with the first input end of a first frequency converter and the first input end of a second frequency converter, the output end of the frequency mixer is respectively and electrically connected with a transmitting antenna, the second input end of the first frequency converter and the input end of a 90-degree phase shifter, and the output end of the 90-degree phase shifter is electrically connected with the second input end of the second frequency converter; the input end of the analog-to-digital converter is respectively and electrically connected with the output end of the first frequency converter and the output end of the second frequency converter;
in step S1, the triangular wave generator generates a periodic triangular wave, and generates a periodic chirp continuous wave according to the triangular wave, where the period of the chirp continuous wave is the period of the triangular wave, and the amplitude of the triangular wave is used to control the frequency of the chirp continuous wave; then, transmitting the linear frequency modulation continuous wave to the mixer; the carrier signal source generates a carrier signal and transmits the carrier signal to the mixer; the frequency mixer mixes the linear frequency modulation continuous wave and the carrier signal to obtain a radio frequency signal, and then the radio frequency signal is respectively sent to the transmitting antenna, the first frequency converter and the 90-degree phase shifter; and the transmitting antenna transmits the radio frequency signal to the front of the vehicle.
6. The target identification method based on the inching characteristic as claimed in claim 5, wherein in step S2, the receiving antenna receives echo signals and sends the echo signals to a first frequency converter and a second frequency converter respectively, the 90-degree phase shifter performs 90-degree phase shift processing on the radio frequency signals and sends the phase-shifted signals to the second frequency converter; the first frequency converter carries out frequency mixing processing on the echo signal and the radio frequency signal to obtain an I channel difference frequency analog signal; and the second frequency converter performs frequency mixing processing on the echo signal and the phase-shifted signal to obtain a Q channel difference frequency analog signal.
7. The target identification method based on the inching characteristic as claimed in claim 4, wherein in step S3, the I channel difference frequency analog signal is represented as I (t), t is a discrete time variable, and the Q channel difference frequency analog signal is represented as Q (t);
in step S4, the digital signal processor combines the I channel difference frequency digital signal I (t) and the Q channel difference frequency digital signal Q (t) into the echo fundamental frequency signal S (t);
in step S4, the distance R of the target and the velocity v of the target are derived:
<math> <mrow> <mi>R</mi> <mo>=</mo> <mfrac> <mi>c</mi> <mrow> <mn>4</mn> <mi>&Delta;f</mi> </mrow> </mfrac> <mfrac> <mrow> <msubsup> <mi>f</mi> <mi>b</mi> <mo>+</mo> </msubsup> <mo>+</mo> <msubsup> <mi>f</mi> <mi>b</mi> <mo>-</mo> </msubsup> </mrow> <mrow> <mn>2</mn> <mi>T</mi> </mrow> </mfrac> </mrow> </math>
v = c ( f b + - f b - ) 4 f 0
where c is the speed of light, Δ f is the maximum frequency offset of the chirped continuous wave, f0Is the center frequency of the chirped continuous wave,forward frequency modulation is used to beat the signal frequency,the beat signal frequency is the negative frequency modulation,andrespectively as follows:
f b + = f t - f r , f b - = f r - f t
wherein f istIs the frequency of the radio frequency signal, frIs the frequency of the echo signal;
in step S5, the speed v of the object is determined, and when the speed v of the object exceeds a set speed threshold, the type of the object is a vehicle; and conversely, when the speed v of the target is less than or equal to the set speed threshold value, the target is classified as a pedestrian.
8. The method for identifying targets based on inching characteristics as claimed in claim 7, wherein in step S5, when a target appears at the corresponding time, the dsp performs time-frequency analysis on the corresponding fundamental echo signal to obtain a time-frequency spectrum S (t, f) of the corresponding fundamental echo signal, where S (t, f) is:
S(t,f)＝∫s(τ)·w(τ-t)·exp(-j2πfτ)dτ
where f denotes a discrete frequency variable, τ a time integral variable, w (t) denotes a window function,
then, a time-frequency graph corresponding to the echo fundamental frequency signal is obtained, and the time-frequency graph corresponding to the echo fundamental frequency signal is a time-frequency graph obtained after S (t, f) discretization;
then, according to the discretized time-frequency graph of S (t, f), obtaining the time-frequency characteristics of the corresponding target, wherein the time-frequency characteristics of the corresponding target are time-frequency entropy f1Or entropy f of the mean instantaneous Doppler spectrum of the corresponding target2，f1Comprises the following steps:
<math> <mrow> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo>=</mo> <mo>-</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>M</mi> </munderover> <munderover> <mi>&Sigma;</mi> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>N</mi> </munderover> <msub> <mi>p</mi> <mi>ij</mi> </msub> <msub> <mi>log</mi> <mn>10</mn> </msub> <msub> <mi>p</mi> <mi>ij</mi> </msub> </mrow> </math>
wherein i and j respectively represent pixel points at the ith row and the jth column position in the time-frequency diagram corresponding to the echo fundamental frequency signal, M and N are respectively the row number and the column number of the time-frequency diagram corresponding to the echo fundamental frequency signal,S(ti,fj) Representing the energy of a pixel point at the ith row and the jth column position in a time-frequency diagram corresponding to the echo fundamental frequency signal;
f2comprises the following steps:
<math> <mrow> <msub> <mi>f</mi> <mn>2</mn> </msub> <mo>=</mo> <mo>-</mo> <munderover> <mi>&Sigma;</mi> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>K</mi> </munderover> <msub> <mi>&rho;</mi> <mi>k</mi> </msub> <msub> <mi>log</mi> <mn>10</mn> </msub> <msub> <mi>&rho;</mi> <mi>k</mi> </msub> </mrow> </math>
wherein,F(fk) Is the kth Fourier transform value of F (f),k is the number of fast Fourier transform points of g (t), S (t, f)k) A column vector formed by all energy values of the kth column in the time-frequency diagram corresponding to the echo fundamental frequency signal, | S (t, f)k) I denotes the pair S (t, f)k) And (6) taking a mold.
9. The method for identifying targets based on inching characteristics as claimed in claim 8, wherein in step S5, after the time-frequency entropy of l targets is obtained through accumulation, the corresponding training samples are obtained according to the time-frequency entropy of each target; when the time-frequency characteristic of the corresponding target is the time-frequency entropy f1When the time-frequency characteristic of the corresponding target is the entropy f of the average instantaneous Doppler spectrum of the corresponding target, the term "M × N" refers to2When l is K; the ith training sample includes: time-frequency characteristic x of ith targetiAnd classification label y of ith targetiI takes 1 to l; when the speed of the ith target exceeds the set speed threshold, yi1, otherwise yi＝-1；
The following optimization problem is then solved:
<math> <mfenced open='' close=''> <mtable> <mtr> <mtd> <munder> <mi>min</mi> <mrow> <mi>w</mi> <mo>,</mo> <mi>b</mi> </mrow> </munder> </mtd> <mtd> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msup> <mrow> <mo>|</mo> <mo>|</mo> <mi>w</mi> <mo>|</mo> <mo>|</mo> </mrow> <mn>2</mn> </msup> <mo>,</mo> </mtd> </mtr> <mtr> <mtd> <mi>s</mi> <mo>.</mo> <mi>t</mi> <mo>.</mo> </mtd> <mtd> <msub> <mi>y</mi> <mi>i</mi> </msub> <mo>[</mo> <mrow> <mo>(</mo> <mi>w</mi> <mo>&CenterDot;</mo> <msub> <mi>x</mi> <mi>i</mi> </msub> <mo>)</mo> </mrow> <mo>+</mo> <mi>b</mi> <mo>]</mo> <mo>&GreaterEqual;</mo> <mn>1</mn> <mo>,</mo> <mi>i</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>,</mo> <mi>l</mi> </mtd> </mtr> </mtable> </mfenced> </math>
w and b are two parameters (scalars) to be solved, and w represents the absolute value of w;
if (w.x)i)+b)>And 0, the ith target is a vehicle target, otherwise, the ith target is a pedestrian target.
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CN113219462A (en) * 2021-04-29 2021-08-06 森思泰克河北科技有限公司 Target identification method and device based on time-frequency diagram and terminal equipment
CN114355337A (en) * 2021-12-31 2022-04-15 北京太格时代自动化系统设备有限公司 Railway construction limit-invasion early warning system based on 24GHz millimeter wave radar technology

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